I vote for the Port-O-Potty. Thirteen years I''ve had one now and lived aboard for seven of those. No through-hulls to leak, no excessive tankage to find a location for, a lot less spare parts to carry around and a simple enough operation that even an idiot can figure it out.
With its siphon-brakes, joker valves and three-way valves, the Marine Toilet is a wonder of the plumbing world. As such, its intricate workings are easily foiled by the ingestion of implements that it can’t handle. Many people are accustomed to tossing “stuff” in their shore-based facility, and they usually don’t think to change their habits when afloat. This has been the cause for many accidents resulting in anything from the need to spend two hours, hunkered over the thing, braking it down and clearing everything out of it to actually causing the boat to sink! You decide which is worse.
For all of its fragile demeanor, it is my opinion that the patent “marine” toilet has no place aboard a boat! K.I.S.S. Go with a Port-O-Potty. Around a hundred bucks for the best model on the market!